Conventionally, phase control dimmers are known which, to provide the dimming control for incandescent bulbs, turns on a switching element (generally, a triac device) at a certain phase angle of an AC supply voltage to readily supply power to incandescent loads with use of one volume resistor element.
In recent years, light-emitting diode driving semiconductor devices for driving a light-emitting diode (hereinafter, referred to as an LED) and light-emitting diode driving apparatuses having the same are developed and put in practical use. In particular, a large volume of lighting devices, such as an LED bulb having a white LED as a light source, are manufactured.
Additionally, of light-emitting diode driving apparatuses, various lighting devices accommodating a phase control dimmer for dimming an incandescent bulb are proposed (e.g., see Patent Literatures (PTLs) 1, 2).
A conventional light-emitting diode driving apparatus disclosed in PTL 1 is in a non-isolated flyback converter circuit structure, and detects a phase angle of a triac having an input pulsating waveform (a time in a zero-crossing state and a half-line cycle time) to adjust a reference signal from a feedback reference circuit. Then, the conventional light-emitting diode driving apparatus controls an LED current in response to the reference signal during the next half-line cycle.
A conventional light-emitting diode driving apparatus disclosed in PTL 2 has a buck converter in which a switching element is disposed on a high side of an input voltage, namely, a “high-side buck converter.”
In general, a buck converter, as compared with a flyback converter, uses a coil rather than a transformer, as an energy conversion circuit. This yields less energy conversion loss at a transformer, producing good conversion efficiency.
Moreover, in the case of a buck converter, the LED current is the same as a coil current and flows during both periods where a switching element is turned on and off. As a result, if amounts of the current in the switching element are the same in the flyback converter and the buck converter, an LED average current is greater in the buck converter, as shown in (b), than the flyback converter. To construct a non-isolated circuit, the use of a buck converter is advantageous in efficiency or cost, as compared with a flyback converter.